1. Field of the Invention
The present invention relates to a pump apparatus such as a fuel pump for use in a vehicle to pump fuel from a fuel tank into an internal combustion engine mounted on the vehicle.
2. Description of the Prior Art
In the field of pumps of the class specified above, various types of pumps have been used, such as displacement type pump (for example, roller pump), centrifugal type pump, axial flow type pump and regenerative pump of "open vane type" to be defined later. The displacement type pumps, such as roller pump, are operative to produce a high pressure (from about 2 to about 3 kg cm.sup.2) and provide a high efficiency. The pumps of this type, however, must be manufactured with a high precision and are very expensive. The pumps of this type, moreover, produce noise and vibration and, in addition, pulsated discharge pressure. The pumps of axial flow type and the centrifugal pumps are not operative to produce such a high pressure as from 2 to 3 kg/cm.sup.2. The regenerative pumps of open vane type are also not operative to produce such a high pressure and, in addition, provide a low efficiency. By the words "open vane type regenerative pump" used in this specification, it is meant to say a regenerative pump in which the bottom face of each of vane grooves formed in one of the end faces of a disc-like impeller intersects with the bottom face of an adjacent vane groove formed in the other end face of the impeller.